The present invention relates to a method for cutting by means of a traveling wire.
Wire electric discharge machines serve for the manufacture of blanking dies, punches, electrodes and extruding dies, but also for the manufacture of small to medium series and often in prototype construction.
Under optimal conditions, modern wire electric discharge machines (WEDM) attain cutting rates of 500 mm2/min in cold work steel. The cutting rate is dependent, inter alia, upon the workpiece height. Reference is made in this regard to the company publication “Experience” No. 23, Id. 027.158, of the company Agie SA, published in October 2003. A qualitative illustration of the cutting rate against the workpiece height will be gathered from the last page (back sheet) of this publication. This somewhat simplified graph starts with the workpiece height of 20 mm, but suggests that the cutting rate fall steeply with a low workpiece height. The illustration of the cutting rate shows a maximum at a workpiece height of approximately 50 mm. In the medium workpiece height range of about 30 to 100 mm, the cutting rate is very close to maximum. The cutting rate falls again with a greater workpiece height.
In WEDM, the dielectric is sprayed into the cutting gap at high pressure for the purpose of discharging the removed particles, specifically, selectively, via the lower wire guide head, the upper wire guide head or both. The width of the cutting gap corresponds to the wire diameter plus double the spark gap width plus wire oscillation, that is to say about 0.05 to 0.5 mm. The flushing liquid is routed directly into the cutting gap, although pressure loss is detectable in the case of a greater workpiece height. The higher the workpiece is, the more difficult the flushing conditions become.
In the case of very small workpiece heights, the conditions are exactly reversed. Gap flushing is highly effective. The contamination of the spark gap is comparatively low, although this is somewhat of a hindrance for a stable process.
The abovementioned characteristic is especially important in the case of low-conductive materials. A relatively good cutting rate can be achieved at small to medium workpiece heights. However, when the workpiece height is relatively large, advance is only very slow.